The varistor is a variety of semiconductor resistors. Varistor has the characteristics of fast response time, low leakage current, excellent voltage ratio, broad voltage-to-energy ratio, low standby power, and no follow-up current, high efficiency surge current handling capability and suppression of voltage stability.

Varistors have high impedance - a few megohms with respect to protected electronic components at rest, and do not alter the design circuit characteristics, but when a transient surge voltage (across the varistor breakdown voltage, The resistance of the varistor will become low (only a few ohms only), and cause the original line short circuit, in other words, is the electronic products or components are therefore protected.

Varistor main purposes: lightning protection, overvoltage protection. If the power transformer into the household side into the zinc oxide arrester can be effective lightning protection, electronic equipment in the power supply input into the varistor, but the voltage will increase the voltage varistor will not resume breakdown short-circuit at the same time the fuse will be disconnected, Thus effectively put over voltage into the circuit board. In the air conditioning line circuit board application varistor most. When the power is 220V when the resistance of the varistor is infinite, when the peak voltage of more than 470V (220V voltage peak is 311V) immediately after the breakdown of short-circuit varistor, the fuse will be fused, the high voltage to enter the equipment side, Thereby effectively protecting the electronic circuit from being infringed. Replace the varistor in the resistor body to be wrapped in insulating material to be protected to prevent arcing. The use of varistors must be installed before the fuse, varistor, but the breakdown of a short circuit is not recoverable, must be replaced. A normal varistor is infinite with a multimeter.